3,960 research outputs found
Amélioration de la gestion des périphériques d'un système embarqué
At CERN, experiments must gather huge amounts of data. The Data Acquisition System of the LHCb is therefore very large, and dedicated to this task. Hundreds of TELL1 boards provide the selection of relevant data and their transfer over a local area network in order to be saved. An embedded system, the Creditcard PC, allows physicists to monitor and program the TELL1 boards. This system runs a CERN release of the Linux operating system, and provides several libraries to handle the communication with the TELL1 board. Several users can work on the same TELL1 board simultaneously. This calls for process synchronization to control the access to the devices. Tests were made progressively, from some dedicated boards to a larger assembly, and then the solution has been distributed to the all TELL1 boards and to other boards using the Creditcard PC
G-300: The first French Getaway Special microgravity measurements of fluid thermal conductivity
Thermal conductivity measurements on liquids are difficult to perform on Earth because of thermal motions due to convection. In microgravity, the convection due to buoyancy is evanescent, and a strong reduction of Rayleigh and Nusselt numbers can be expected. Three low viscosity liquids are selected to carry out the measurements; distilled water (standard) and two silicone oils. A modified hot plate method with a simplified guard ring is used; the reduction of convective motions permitted the use in the experimental cells of larger interplate distances and/or temperature differences than in Earth measurements, improving the accuracy. Comparisons between Earth and orbit results may help to understand the convection occurrence in the cells. Thermal, vibrational, and EMI tests have proved that the design satisfies the NASA requirements
Robust seismic velocity change estimation using ambient noise recordings
We consider the problem of seismic velocity change estimation using ambient
noise recordings. Motivated by [23] we study how the velocity change estimation
is affected by seasonal fluctuations in the noise sources. More precisely, we
consider a numerical model and introduce spatio-temporal seasonal fluctuations
in the noise sources. We show that indeed, as pointed out in [23], the
stretching method is affected by these fluctuations and produces misleading
apparent velocity variations which reduce dramatically the signal to noise
ratio of the method. We also show that these apparent velocity variations can
be eliminated by an adequate normalization of the cross-correlation functions.
Theoretically we expect our approach to work as long as the seasonal
fluctuations in the noise sources are uniform, an assumption which holds for
closely located seismic stations. We illustrate with numerical simulations and
real measurements that the proposed normalization significantly improves the
accuracy of the velocity change estimation
Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films
X-ray photoelectron diffraction is used to directly probe the intra-cell
polar atomic distortion and tetragonality associated with ferroelectricity in
ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab-initio
calculations, unambiguously demonstrate non-centro-symmetry in films a few unit
cells thick, imply that films as thin as 3 unit cells still preserve a
ferroelectric polar distortion, and also show that there is no thick
paraelectric dead layer at the surface
Extragalactic database. VII Reduction of astrophysical parameters
The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main
astrophysical parameters for more than 100,000 galaxies. The most common names
are compiled allowing users to recover quickly any galaxy. All these measured
astrophysical parameters are first reduced to a common system according to well
defined reduction formulae leading to mean homogeneized parameters. Further,
these parameters are also transformed into corrected parameters from widely
accepted models. For instance, raw 21-cm line widths are transformed into mean
standard widths after correction for instrumental effect and then into maximum
velocity rotation properly corrected for inclination and non-circular velocity.
This paper presents the reduction formulae for each parameter: coordinates,
morphological type and luminosity class, diameter and axis ratio, apparent
magnitude (UBV, IR, HI) and colors, maximum velocity rotation and central
velocity dispersion, radial velocity, mean surface brightness, distance modulus
and absolute magnitude, and group membership. For each of these parameters
intermediate quantities are given: galactic extinction, inclination,
K-correction etc..
All these parameters are available from direct connexion to LEDA (telnet
lmc.univ-lyon1.fr, login: leda, no passwd
OR http://www-obs.univ-lyon1.fr/leda ) and distributed on a standard CD-ROM
(PGC-ROM 1996) by the Observatoire de Lyon via the CNRS (mail to
[email protected]).Comment: 13 pages, 12 figures. The CDROM of the extragalactic database LEDA is
available by mailing to: [email protected]
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